DE102010042349A1 - Manufacturing semi-finished textile product from carbon fibers obtained from matrix material, comprises manufacturing non-woven fabric and/or fleece, and impregnating non-woven fabric and/or fleece with matrix material - Google Patents

Abstract

Manufacturing a semi-finished textile product from carbon fibers obtained from a matrix material, comprises: (a) manufacturing a non-woven fabric composed of at least 10% carbon fibers and/or a fleece composed of at least 10% carbon fibers, where at least a portion of the fibers used for the manufacturing of the fabric or fleece, are waste fibers and/or recycling fibers; and (b) impregnating the non-woven fabric and/or fleece with a matrix material comprising thermoplastic material, thermoset materials and/or elastomers. Independent claims are included for: (1) the semi-finished textile product, preferably prepreg, comprising carbon fibers pre-impregnated with the matrix material; and (2) a carbon fiber reinforced composite material obtained by hardening or thermally deforming and optionally after compacting the semi-finished textile product.

Description

The present invention relates to a process for producing a textile semifinished product, in particular a prepreg, from carbon fiber preimpregnated with a matrix material, a textile semifinished product obtainable by this process, in particular prepreg, and its use in particular for the production of composite components, in particular for the production of Exterior skin and structural components for motor vehicles and transport vehicles.

Carbon fiber-containing composite materials, such as carbon fiber reinforced plastic (CFRP), which is composed of an example of phenolic resin or epoxy resin matrix in which carbon fibers or graphite fibers embedded in one or more fiber layers, or carbon fiber reinforced carbon (CFC), which consists of a carbon matrix , in which carbon fibers or graphite fibers are embedded in one or more fiber layers, have a high strength and rigidity, especially in the fiber direction and are also characterized by a low weight compared to other materials, such as steel, by a low Thermal expansion and excellent thermal shock resistance. Because of these advantageous properties, composite materials containing such carbon fibers are used in many technical fields and in particular increasingly in the automotive industry, for example, as a material for structural components or for outer skin components of a motor vehicle.

However, the composite materials currently used for this have a number of disadvantages.

For example, automotive structural members are typically fabricated from carbon fibers in the form of composites containing anisotropic gusset structures. However, structural components are often exposed to isotropic load conditions, which is why these composites are often made up of several, with each other specifically oriented gel layers, to take into account these isotropic load conditions. Therefore, the manufacturing process for such composites is very expensive, which is why these composites are expensive. Another disadvantage of these materials is their comparatively poor drapability.

On the other hand, outer skin components or visible components of motor vehicles are usually made of composite materials which contain carbon fibers in the form of tissue structures. These can be produced comparatively inexpensively by a resin injection process (RTM process, "Resin Transfer Molding" process). However, these materials have, inter alia, an unsatisfactory surface quality. For example, the surface quality is adversely affected by the fact that an increased shrinkage of the matrix material occurs at the crossing points of the fabric, as a result of which the fabric structure is visible on the surface of the composite material.

For these reasons, there is a need for composites containing carbon fibers which have improved properties, such as, in particular, better surface quality and better drapability, which are of comparatively simple construction, and which can be produced comparatively inexpensively. In particular, there is a need for semi-finished products, in particular a prepreg, from corresponding composite materials, which can be easily and inexpensively processed to the desired end products, and for a method by which such semi-finished products, in particular prepregs or end products made of composite materials are produced easily and inexpensively can.

In particular, there is a need for corresponding materials which have as high as possible a content of recycled fibers in order to meet the recycling rate for motor vehicles required in the ELV Act, and for manufacturing processes therefor.

The object of the present invention is therefore to provide a process for producing a textile semifinished product, in particular a prepreg, from carbon fibers preimpregnated with a matrix material, which can be carried out simply and inexpensively, in which a high proportion of recycled fibers can be used, and which leads to a textile semi-finished product, which has an excellent surface quality and good drapability.

• a) Herstellen von aus wenigstens 10% Carbonfasern bestehendem Vlies und/oder von aus wenigstens 10% Carbonfasern bestehendem Filz, wobei wenigstens ein Teil der zur Herstellung des Vlieses und/oder Filzes eingesetzten Fasern Abfallfasern und/oder Recyclingfasern sind, und
• b) Imprägnieren des Vlieses und/oder des Filzes mit einem Matrixmaterial, welches aus der Gruppe ausgewählt wird, welche aus Thermoplasten, Duroplasten, Elastomeren und beliebigen Mischungen von zwei oder mehr der vorgenannten Materialien besteht.

According to the invention, this object is achieved by a method for producing a semi-finished textile product, in particular a prepreg, from carbon fibers preimpregnated with a matrix material, which comprises the following steps:

• a) producing from at least 10% carbon fibers existing fleece and / or made of at least 10% carbon fibers felt, wherein at least a portion of the fibers used for the production of the fleece and / or felt are waste fibers and / or recycled fibers, and
• b) impregnating the web and / or felt with a matrix material selected from the group consisting of thermoplastics, thermosets, elastomers and any mixtures of two or more of the foregoing.

With the method according to the invention, textile semi-finished products, in particular prepregs, can be produced in a simple and cost-effective manner from carbon fibers preimpregnated with a matrix material with a high proportion of recycled fibers and / or waste fibers and with excellent drapability, which can be easily and inexpensively converted into the desired end products with high yields Strength and stiffness can be processed at a comparatively low weight and with an excellent surface quality. The use of a nonwoven or felt in process step a) can set a targeted anisotropy of the properties, in particular the strength and rigidity, of the semifinished product and the end product subsequently produced therefrom. In addition, the use of a nonwoven or felt in method step a) yields a semifinished product with excellent drapability, which is considerably better than the drapability of a semifinished product which contains exclusively knitted fabric or woven fabric as the fiber material. Finally, the method according to the invention allows a closed or at least virtually closed recycling loop by the use of waste fibers or waste fibers and / or recycled fibers. Since in the inventive method on the use of newly produced carbon fibers whose production is very complex and energy-intensive, is omitted or their amount is at least greatly reduced, but instead recycled fibers and / or waste fibers are used, the inventive method is also cheaper than the known from the prior art method for producing corresponding semi-finished products, in which new fibers are used. Consequently, the process according to the invention is not only a process for the production of a semifinished product from carbon fibers preimpregnated with a matrix material, but in particular also a process for the recycling or recycling of used fibers and / or waste fibers.

For the purposes of the present invention, recycled fibers are understood to mean fibers which have been produced from used fibers, the used fibers being able to originate from any used fiber material, such as, for example, woven fabrics, knitted fabrics, such as knitted or knitted fabrics, loops, fiber mats, from fiber strands, from felts, from nonwovens or from composite materials, such as CFC, CFRP, carbon fiber reinforced concrete or the like.

In addition, the term waste fiber referred to in the context of the present invention, a fiber which has been obtained from production waste, such as waste, production committee and the like, including from Neufasermaterial, wherein the production waste can be any fiber material, such as fabric, knitted fabric, knit, scrim , Fiber mat, fiber strand, felt, nonwoven and / or composite material such as CFC, CFRP, carbon fiber reinforced concrete, prepreg or the like.

For the purposes of the present invention, a carbon fiber is understood as meaning a fiber which consists of at least 90%, preferably at least 95%, more preferably at least 98%, very preferably at least 99%, and most preferably entirely from carbon.

According to a particularly preferred embodiment of the present invention, the impregnation of the nonwoven and / or felt with the matrix material in step b) is carried out by a process selected from the group consisting of prepreg process, wet press process, resin infusion process, film lamination process and vacuum ("Vacuum Assisted Resin Infusion" or VARI) procedure. Surprisingly, an excellent impregnation of the carbon fiber fleece or of the carbon fiber felt can be achieved by each of the abovementioned processes, as a result of which textile semifinished product is obtained, in which the fiber material is embedded particularly homogeneously in the matrix. Due to the quasi-isotropic orientation of the fibers in the plane and the homogeneous distribution of the matrix shrinkage optical abnormalities can be prevented. This was surprising because nonwovens and felts are basically very difficult to impregnate due to their low permeability in the fiber direction. Such good impregnation, let alone homogeneous embedding of fibers in the matrix, is not possible with other techniques, such as the RTM process, where the injection or resin spreading of the matrix occurs along the textile orientation.

Particularly good results are achieved in this regard, in particular, if the impregnation of the web and / or the felt with the matrix material in step b) by a liquid prepreg process liquid or semi-liquid polymers or oligomers, by a powder prepreg process or by a wet pressing process is performed.

In principle, fiber blends of new fibers and waste fibers and / or recycled fibers with any ratios of new fibers to the waste fibers and / or recycled fibers can be used in step a) of the process according to the invention, provided that this ensures that a nonwoven comprising at least 10% carbon fibers and / or or a felt consisting of at least 10% carbon fibers is obtained. In order to keep the recycling rate as high as possible, it is proposed in a development of the invention that in process step a) for the production of the fleece and / or the felt, a fiber mixture is used, which is at least 20%, preferably at least 50%, particularly preferred at least 80%, more preferably at least 90%, most preferably at least 95% and most preferably entirely consists of waste fibers and / or recycled fibers.

Depending on the application, a more or less high proportion of carbon fibers may be required in the semifinished product, based on the total fiber content. Good results are obtained, in particular, when the total fiber content of the carbon fiber amount is at least 20%, preferably at least 40%, more preferably at least 60%, more preferably at least 80%, most preferably at least 90% and most 100%.

Accordingly, the proportion of carbon fibers in the waste fibers and / or recycled fibers used in process step a) can also vary. Only for example, in the process step a) waste fibers and / or recycled fibers may be used, of which at least 10%, preferably at least 30%, more preferably at least 60%, most preferably at least 80% and most preferably 100% consist of carbon fibers. The remaining waste fibers and / or recycled fibers may be made of any material, such as glass and / or cotton.

If a fiber mixture is used in process step a) which contains not only waste fibers and / or recycled fibers but also newly produced carbon fibers, these can be produced, for example, by first spun fibers from carbonaceous starting materials, such as pitch, polyacrylonitrile, oxidized polyacrylonitrile or cellulose before they are subsequently carbonized under drawing and optionally graphitized, before the fibers thus produced finally surface-treated if necessary and optionally coated with sizing.

Not only monofilaments can be used as starting material for the production of the nonwoven or felt, but in particular also bifilaments or mixtures of two or more mono- and / or bifilaments. It is also possible, for example, to use stretch-torn filaments or fibers. In particular, mixtures of carbon fibers and fibers of a thermoplastic can be used for the production of the nonwoven or felt, which later allows a direct consolidation of the textile semifinished product to form an organic sheet.

Preferably in the step a) for the production of the fleece and / or the felt fibers with a length between 1 and 500 mm, particularly prefers fibers with a length between 5 and 500 mm, very particularly prefers fibers with a length between 10 and 250 mm and most preferably used fibers having a length between 20 and 220 mm. Alternatively, blends of short cut fibers having a length between 1 and 5 mm and long fibers with a length between 5 and 500 mm, particularly preferably long fibers with a length between 10 and 250 mm and all may be used to produce the carbon fiber-containing nonwoven and / or felt particularly preferred are long fibers having a length between 20 and 220 mm.

The waste fibers and / or recycled fibers can be made in any conceivable way from waste fiber material or from used fiber material. For example, the recycled fibers may be made from a fibrous material preimpregnated with a matrix material, or composite containing fibers, such as CFC or CFK, by comminuting the fiber material preimpregnated with a matrix material or the composite containing fibers before the fibrous material is then crushed the matrix material is dissolved and separated. The comminution is preferably carried out with a shredder, with a granulator, with an impact mill or with a hammer mill so that particles with a length between 1 and 500 mm are obtained.

In this embodiment, the dissolution of the matrix of the carbon fibers, for example by solvolysis, that is, by contacting the material with an acid, for example with a mineral acid, such as sulfuric acid or nitric acid, with an alkali such as sodium hydroxide, or with a solvent. Alternatively, the dissolution of the matrix from the carbon fibers may inevitably occur during comminution. According to a further alternative, the removal of the matrix can also be effected by pyrolysis of the matrix material. Thereafter, the matrix can be separated from the carbon fibers by, for example, screening or sifting, the sizing being performed, for example, in a rotary sifter, air classifier or zigzag sifter. Finally, the fiber material obtained can still be coated with size.

According to a further preferred embodiment of the present invention, the previously described, consisting of at least 10% carbon fibers nonwoven and / or made of at least 10% carbon fibers felt in the inventive method in combination with at least one other fiber material is used, wherein the other fiber material preferably made is selected from the group consisting of woven, laid, unidirectional (UD) strands, tapes, nonwovens, felts, and any mixtures of two or more of the foregoing materials. These fiber materials have a higher mechanical stability and in particular a higher tensile strength than the nonwoven fabric produced in process step a) and consisting of at least 10% carbon fibers and / or the felt consisting of at least 10% carbon fibers, for which reason the nonwoven fabric is produced by such a combination of different fiber materials mechanically stabilized. As a result, in carrying out the method according to the invention and in particular in carrying out the method step b) any resulting stresses are absorbed by the other fiber material, so that the web or the felt is exposed to only low tensile stresses and thus damage or even destruction of the web or Felt is reliably prevented so that it can be processed deformation-free and non-destructive to the semi-finished textile product and then from this to the final product.

In the aforementioned embodiment, the individual fiber materials may be arranged in the form of a laminate or, if possible, the individual fiber materials may be combined together in one layer. An example of the latter case is forfeiture of nonwoven and scrim, whereas examples of a laminate structure are nonwoven / fabric / nonwoven or nonwoven / nonwoven / nonwoven structures. In principle, the laminate may consist of at least one nonwoven layer and at least one fabric layer, at least one nonwoven layer and at least one release layer or a nonwoven fabric with core material, wherein the core material may be, for example, foam, have a honeycomb structure, may be a cardboard core or any other core material can be. In this case, the nonwoven or felt layers in such laminates are preferably located on the outer sides of the laminate, so that the textile semifinished product or the end product produced therefrom has the advantageous surface properties resulting from the use of fleece or felt compared to woven fabric and knitwear.

In order to keep the recycling rate as high as possible, it is proposed in development of the invention that the other, selected from the above group fiber material consists at least partially of waste fibers and / or recycled fibers, the proportion of waste fibers and / or recycled fibers based on the total amount the fibers in the other fibrous material is preferably at least 20%, more preferably at least 50%, further preferably at least 80%, most preferably at least 90%, most preferably at least 95% and most preferably 100%.

In a further development of the inventive concept, it is proposed, as another, selected from the above group fiber material to use a fiber material which consists of carbon fibers, glass fibers, polymer fibers and mixtures of two or more of the aforementioned materials. Examples of suitable polymeric fibers include, but are not limited to, polyamide fibers, polyester fibers, polypropylene fibers, polyacrylonitrile fibers, oxidized polyacrylonitrile fibers, as well as fibers of copolymers of two or more of the foregoing materials and blends of two or more of the foregoing materials. Such fiber materials have a high mechanical strength and are therefore ideal as the nonwoven and / or the felt mechanically stabilizing fiber material.

In this case, combining, ie in the case of forming a combination of the two fiber materials in one layer, mixing the two fiber materials and, in the case of forming a laminate structure, laminating the two fiber material layers, that is, combining at least 10% carbon fibers Web and / or the felt consisting of at least 10% carbon fibers and, secondly, the at least one other fiber material selected from the above group, during the process step b), ie during the impregnation, or before the impregnation, wherein combining the two fiber materials is preferred before impregnation. If the fleece or the felt are combined in a layer with each other, such as in In the case of forfeiture of fleece and scrim, the combination of the two fiber materials can be carried out particularly preferably also in the nonwoven or felt production in process step a).

In principle, all thermoplastics, thermosets and elastomers, in each case individually or in a mixture with one another, can be used as the matrix material in process step b). However, good results are obtained particularly when the matrix material is selected from the group consisting of epoxy resins, phenolic resins, vinyl ester resins, polyester resins, polyurethane resins, benzoxazine resins, novolaks, cyanate ester resins, bismaleimide resins, bisoxazolines, polyolefins such as polypropylene, engineering thermoplastics such as polyamides , and any mixtures of two or more of the aforementioned materials.

In a further development of the inventive concept, it is proposed to impregnate the nonwoven or the felt in method step b) with so much matrix material that the semifinished product after method step b) has a content of matrix material between 1 and 90% by weight, more preferably between 30 and 70 wt .-% and most preferably between 40 and 65 wt .-%.

As stated above, the impregnation of the nonwoven fabric and / or the felt with the matrix material in step b) is carried out by a method selected from the group consisting of prepreg process, wet press process, resin infusion process, film lamination process and vacuum assisted (VARI) Surprisingly, a good impregnation of the hard to be impregnated carbon fiber nonwoven or the carbon fiber felt is achieved by each of the above methods. In this case, particularly good results are obtained if the impregnation of the nonwoven and / or the felt with the matrix material in step b) is carried out by a powder prepreg process, by a liquid prepreg process or by a wet pressing process.

In the wet pressing process, a blank of the web or felt produced in process step a) is placed in an open mold before liquid or solid matrix material is poured, sprayed, spread or laid onto the web or felt before the mold is closed and in the mold, a pressure of preferably between 0.1 and 1000 bar is applied. Due to the pressure in the mold, the same flow paths result on all sides, which is why the matrix material in the nonwoven or in the felt evenly distributed.

Very particularly preferably, the impregnation of the nonwoven and / or the felt with the matrix material in process step b) is carried out by a powder prepreg process and most preferably by a liquid prepreg process. If a powder prepreg process is used, this is preferably with liquid matrix systems having a viscosity at room temperature of 10 to 1,000,000 mPa · s, more preferably having a viscosity at room temperature of 400 to 100,000 mPa · s, and most preferably having a viscosity at room temperature from 1,000 to 25,000 mPa · s performed.

In order to avoid the effect of excessive tensile forces on the nonwoven or the felt in the prepreg process, this may be carried out independently of whether this is carried out as a powder prepreg process or as a liquid prepreg process, preferably that the nonwoven or the Felt before performing the process step b) on one side or, if the nonwoven or the felt is used without the other fiber material, also on both sides with a support material, preferably with a carrier film or with a backing paper coated. The carrier film may for example be composed of a thermoplastic and may be, for example, a film or a film made of polyester. In this case, the thermoplastic film or the thermoplastic film may in turn be coated.

Alternatively, carrier paper can be used for this purpose, which preferably has a grammage or a basis weight of 10 to 300 g / m ² and particularly preferably from 50 to 130 g / m ² .

In the case of a thermoplastic carrier film, the carrier material can be applied, for example by calendering, to the nonwoven or to the felt.

If the impregnation of the fleece and / or the felt with the matrix material in the process step b) by a powder prepreg process, the matrix material is applied in powder form on the fleece or the felt, which, for example, by immersing the fleece or felt in a impregnating bath containing a powder suspension, by direct sprinkling of the powder on the nonwoven or the felt or by electrostatic bonding can take place. In this case, the order of the powdery matrix material, in particular with the latter two methods, selectively on one side of the nonwoven or felt, or this may be done, which is preferred, in particular with the former method, on both sides of the textile fabric.

When the matrix material is a thermoplastic, the powdery matrix material applied to the nonwoven or felt is preferably fixed by fusing onto the nonwoven or felt, the fusing being effected by, for example, passing the powder coated nonwoven or felt through a temperature just above the Melting temperature of the thermoplastic set heating zone can take place. As a result, in the subsequent method steps, a drop of the powder from the nonwoven or felt can be reliably prevented.

In a further embodiment, the matrix material is a thermoset. This is preferably applied to the web or felt in the form of a powdered thermoset prepolymer before the powdered material is melted, preferably at a temperature just above the melting temperature of the thermoset prepolymer but below the crosslinking temperature of the thermoset prepolymer on the web or felt is fixed. A thermoset prepolymer according to the present invention, in accordance with the standard definition of this term, is understood as meaning an oligomer or polymer which can be converted into a thermoset via crosslinking. In this case, the crosslinking, if the thermosetting prepolymer is sufficiently functionalized, without crosslinking agent, or this can be done with a crosslinking agent. As the crosslinking agent, there may be used, for example, a compound selected from the group consisting of amines, for example, hexamethylenetetramine, acid anhydrides, Lewis acids, radical formers, such as, in particular, peroxides, azo compounds and the like, transition metal compounds, such as transition metal salts, transition metal organic compounds and the like Acids, inorganic acids and any mixtures of two or more of the aforementioned compounds. Vinyl esters and polyesters are suitable as crosslinking agents, in particular free-radical formers and transition metal compounds, whereas phenol resins are suitable as crosslinking agents, in particular amines, inorganic acids and organic acids and suitable for the other matrix precursors from the above list as crosslinking agents, in particular amines, acid anhydrides and Lewis acids.

If the matrix material is a thermosetting material, it is preferably thermally and / or chemically pre-crosslinked prior to subsequent complete curing, preferably after application and after fixation, resulting in an increase in molecular weight, as a result of which this material achieves greater stability.

If the impregnation of the fleece and / or the felt with the matrix material in process step b) is carried out by a liquid prepreg process, the matrix material can be applied to the fleece or the felt, for example by spraying, dipping, sprinkling or brushing, either directly or indirectly, a solution containing the matrix material, suspension, emulsion or hot melt are applied.

Regardless of whether the prepreg process is carried out as a powder prepreg process or as a liquid prepreg process, the impregnation in process step b) is preferably carried out by a pressure-temperature treatment, that is to say at elevated temperature and at elevated pressure.

It is further proposed in a further development of the inventive concept, to carry out the impregnation in process step b) at a temperature which is 1 to 400 ° C, preferably 10 to 200 ° C and preferably 30 to 150 ° C above the glass transition temperature of the uncrosslinked matrix material.

A further subject of the present invention is a semifinished textile product, in particular prepreg, of carbon fibers preimpregnated with a matrix material, which is obtainable by the method described above.

Such a semifinished textile product thus consists of a matrix material which is selected from the group consisting of thermoplastics, thermosets, elastomers and any mixtures of two or more of the aforementioned materials, wherein in the matrix a fleece and / or felt is embedded, the nonwoven or the felt consists of at least 10% carbon fibers and contains waste fibers and / or recycled fibers.

According to a preferred embodiment of the present invention may be embedded in the matrix material, another fiber material, which is preferably selected from the group which of woven, laid, unidirectional (UD) strands, tapes, nonwovens, felts and any mixtures of two or more of the aforementioned materials.

The semifinished textile product according to the invention is characterized in that it can be produced simply and cost-effectively, using high proportions of recycled fibers and / or waste fibers. Further, the semi-finished textile of the present invention has excellent drapability, and therefore, it can be easily and inexpensively processed into the desired end product having high strength and rigidity at comparatively low weight and excellent surface quality. In particular, in the textile semifinished product according to the invention, due to the use of a nonwoven or felt, by introducing a gradable preferred orientation during the production of the nonwoven, a targeted anisotropy of the properties, in particular of the strength and the stiffness, can be set.

According to a particularly preferred embodiment of the present invention, the semifinished textile product according to the invention is selected by a process selected from the group consisting of prepreg process, wet pressing process, resin infusion process, Folienkaschierverfahren and vacuum assisted (VARI) method and most preferably by a powder prepreg process, by a liquid Prepreg process or produced by a wet pressing process. Surprisingly, in the semifinished textile product according to the invention thus produced, the fiber material is embedded in the matrix in a particularly homogeneous manner, as a result of which the resin shrinkage during hardening of the matrix can be at least almost completely prevented.

The semifinished textile product according to the invention can be recycled directly or in a consolidated form into the production process. Exemplary applications are the production of a structural component or an outer hull component of a motor vehicle, a rail vehicle or a transport vehicle from the textile semifinished product.

Another object of the present invention is a carbon fiber reinforced composite, which is obtainable by curing a crosslinking matrix of the textile semi-finished product described above.

The curing is carried out depending on the matrix material used specifically preferably at a temperature between 0 and 300 ° C and more preferably at a temperature between 25 and 200 ° C.

Furthermore, the present invention relates to a carbon fiber-reinforced composite material which is obtainable by thermoforming and optionally recompressing a thermoplastic matrix of the textile semifinished product described above.

In this case, the thermal forming and the densification depending on the specific matrix material used, for example, in the case of a matrix material of semi-crystalline thermoplastic preferably at a temperature between 0 and 200 ° C and more preferably at a temperature between 25 and 100 ° C above the melting temperature of the thermoplastic and, for example, in the case of a matrix material of amorphous thermoplastic, preferably at a temperature between 0 and 400 ° C and more preferably at a temperature between 10 and 200 ° C above the glass transition temperature of the thermoplastic.

According to a preferred embodiment of the present invention, the carbon fiber reinforced composite according to the invention has a fiber content between 20 and 60%, preferably between 30 and 50%, more preferably between 35 and 45% and most preferably of 40%.

Furthermore, it is proposed in a development of the inventive idea that the carbon fiber reinforced composite material has a tensile strength of 100 to 2000 N / mm ² and preferably 200 to 800 N / mm ² and / or a modulus of elasticity of 5 to 180 GPa and preferably from 10 to 80 GPa having.

Finally, the present invention relates to the use of the textile semifinished product described above for the production of components, such as a structural component or a Außenhaubauteils a motor vehicle, a rail vehicle or a transport vehicle.

Hereinafter, the present invention will be further described by way of these illustrative but nonlimiting examples.

Examples

Example 1 Production of a Prepreg Based on Carbon Fiber Nonwoven Made from Processing Waste and a Matrix of Epoxy Resin and Further Processing

On a laboratory coating plant was from a carbon fiber fleece, which consisted of carbon fiber wastes from SGL ACF GmbH, Germany, and from a liquid epoxy resin formulation of the SGL Group called FT-109-1, which by curing at a temperature between 80 and 150 ° C is characterized at an achievable glass transition temperature of up to 120 ° C, a prepreg produced.

The carbon fiber fleece was produced with a basis weight of about 103 g / m ² from waste from filament bundles with a length between 20 and 250 mm in the carbon fiber-based textile production, namely through the operations of comminuting the waste waste, opening the filament strands, mixing the opened filament strands, combing, applying an adhesive material, namely an adhesive fleece, packaging and winding. The carbon fibers had one according to the ASTM D5291-02 determined carbon content ("carbon content") of more than 90 wt .-% based on the total weight of the fibers. Further, the carbon fiber nonwoven contained a small amount of cotton and polyester yarn whose content did not exceed 20%. Furthermore, the carbon fibers were pre-oriented in nonwoven production, so that a certain anisotropy in terms of fiber orientation and thus the mechanical properties was adjusted.

The coating system consisted of a respective unwinding unit for coating paper or carrier paper and the carbon fiber fleece, a coating unit, a first calender, a furnace unit, a second calender, a cooling plate and a take-up unit. After applying a film of the epoxy resin to the coating paper having a very defined grammage of 115 g / m ² (+/- 3 g / m ² ), the carbon fiber nonwoven fabric was deposited in the resin film and consolidated in the first calender to a first impregnation. Thereafter, the pre-impregnated semi-finished product was placed in a set to 130 ° C oven in which on the one hand by the decreasing with increasing temperature viscosity of the resin and the suction effect of the nonwoven by this the actual impregnation took place and geststock gestagen to the other, that is prepolymerized. The achieved degree of polymerization was 40%. The still-hot prepreg was then passed through the second calender unit for further compaction, then cooled down on a cold plate until the prepreg temperature was reduced to less than 40 ° C, and finally wound up in the take-up unit under a tension of 450N.

Then, the prepreg thus prepared was processed into a carbon fiber reinforced plastic (CFRP) comprising the nonwoven made of carbon fiber derived from production wastes. For this purpose, several layers of the prepreg were cut to square pieces on a guillotine and centered symmetrically on each other. Subsequently, the carbon fiber nonwoven prepreg was first pressed at a temperature of 160 ° C for 1 hour under a pressure of 42 bar. In principle, the pressing at temperatures of 130 to 180 ° C over a period of up to one hour and under a pressure of more than 0.1 bar, preferably from 1 to 100 bar, more preferably from 5 to 30 bar are performed.

With the above method, various CFC's were prepared by varying the temperature used in the curing and the duration of the curing, each obtaining very homogeneous composite sheets. The concrete curing conditions in the individual experiments and the characteristic values of the composite plates produced are summarized in Table 1 below: TABLE 1 Carbon fiber nonwoven prepreg values Total weight per unit area: 218 g / m ² +/- 20 g / m ² DIN EN 2557 Fiber areal weight: 103 g / m ² +/- 15 g / m ² DIN EN 2329 Resin content: 115 g / m ² +/- 3 g / m ² DIN EN 2559 Resin: FT-109-1 Epoxy resin - hardening Depending on the curing conditions, the glass transition temperature reached > 90 ° C 15 min @ 130 ° C DMA, RT-200 ° C at 3 K / min; Onset E ' > 110 ° C 60 min @ 130 ° C > 98 ° C 15 min @ 150 ° C > 93 ° C 15 min @ 180 ° C

For the above four samples, the 3-point flexural strength, the 3-point flexural modulus, the elongation at break, the density and the fiber volume content were determined. The measuring methods used for this purpose and the results obtained for the sample cured at 130 ° C. for 60 minutes are summarized in Table 2 below. measurement parameters measurement methods unit test direction Average Deviation (+/-) 3-point bending strength ISO-14125 MPa 0 ° 563.6 34.1 3-point flexural modulus ISO-14125 MPa 0 ° 32200 900 elongation ISO-14125 % 0 ° 1.9 0.1 density DIN / EN / ISO 1183-1 g / cm ³ - 1.37 0.01 Fiber volume content DIN / EN 2564 % Vol. - 35.55 1.83

Comparable values were obtained with the other three samples.

For the sake of completeness, it should be noted that in the method described above, as an alternative to the epoxy resin, a thermoplastic or thermosetting resin system or other thermosetting resin system may be used, in the form of a solution in an inorganic or organic solvent. For this purpose, preferred solvents are ketones, such as acetone and methyl ethyl ketone, alcohols, ethers, esters and the like. The procedure for the impregnation is analogous to the previously described method and differs therefrom only in that in the furnace, in contrast to the previously described variant, only the solvent is removed by evaporation.

Example 2 Production of a Carbon Fiber Reinforced Plastic Based on a Carbon Fiber Fleece of Recycled Carbon Fibers by Wet Pressing

version 1

A carbon fiber fleece produced from production wastes as described in Example 1 was processed by means of a wet pressing process into carbon fiber reinforced plastic (CFRP).

For this purpose, several layers of the fleece were cut into square pieces on a leverage cutting machine and placed in a mold center-symmetrically on each other. Subsequently, an amount of epoxy resin formulation calculated to the desired fiber volume content of 35% in the finished part was added to the mold. Thereafter, the mold was closed and pressed at a temperature of 150 ° C for 2.5 hours at a pressure of 42 bar. Basically, the pressing in this system at a temperature of 100 to 150 ° C over a period of up to 3 hours, preferably up to one hour and more preferably of up to 15 minutes and under a pressure of 0.1 to 1000 bar , preferably be carried out from 1 to 100 bar and more preferably from 5 to 30 bar.

As a result, very homogeneous composite panels were obtained.

Variant 2

A carbon fiber nonwoven made from production waste carbon fibers as in Example 1 was processed by a wet pressing process to carbon fiber reinforced plastic (CFRP).

For this purpose, several layers of the web were cut into square pieces on a lever cutting machine and stored in a mold alternately with a respective resin layer between two carbon fiber fleece layers centered symmetrically on each other. The resin layers were sprayed on, but could also be poured into the mold in the form of a resin film. Subsequently, the mold was closed and pressed at a temperature of 150 ° C for 1 hour and under a pressure of 42 bar.

As a result, very homogeneous composite panels were obtained.

Example 3 Production of a Prepreg Based on Carbon Fiber Fabric Made from Processing Waste and Further Processing into a Thermoplastic Material

On a laboratory coating plant, a prepreg was produced from a carbon fiber fleece which consisted of carbon fiber waste waste from SGL ACF GmbH, Germany, and a solid, thermoplastic polymer matrix made from polyamide 6.

The carbon fiber fleece had a basis weight of about 103 g / m ² and consisted in the carbon fiber-based textile production waste waste from filament bundles with a length between 20 and 250 mm and this was through the steps crushing the waste trimmings, opening the filament strands, mixing the open filament strands, combing, applying an adhesive material, namely an adhesive nonwoven fabric, packaging and winding produced. The carbon fibers had one according to the ASTM D5291-02 determined carbon content ("carbon content") of more than 90 wt .-% based on the total weight of the fibers. Further, the carbon fiber nonwoven contained a small amount of cotton and polyester yarn whose content did not exceed 20%.

The coating system consisted of a respective unwinding unit for coating paper or carrier paper and the carbon fiber fleece, a coating unit, a first calender, a furnace unit, a second calender, a cooling plate and a take-up unit.

Carbon fiber webs and matrix materials prepared as described above were combined by each of the three methods described below.

Variant 1 - powder prepreg

The coating system in this case consisted of a winding and unwinding unit, a powder spreader and a heating field. After applying the powdery matrix material to the carbon fiber nonwoven fabric, this assembly was placed in the heating field with the temperature of the heating field set at 130 ° C and the conveying speed of the structure through the heating field adjusted so that the powder grains were sintered, i. H. that these at least melt on their surface or even completely melted. As a result, an adhesion of the powder to the carbon fiber fleece was achieved. In this process, however, no significant impregnation of the web took place.

Following the first coating and fixing, a second coating was carried out analogously to the above-described procedure on the previously uncoated side. Due to the double-sided coating, a particularly high degree of uniformity and flatness of the powder prepreg has been achieved. However, this process step is optional.

The powder prepreg produced in this way had a basis weight of 218 g / m ² .

Some of the powder prepregs produced in this way were finally consolidated or heated or impregnated by heated calenders, the temperature being 100 ° C. above the glass transition temperature of the polymer used.

As a result, the polymer was introduced into the carbon fiber nonwoven and compacted to an organic sheet. Subsequently, the consolidated organo sheet was cooled down and wound up or cut into sheets.

Variant 2 - foil lamination

In this variant, the thermoplastic polymer, which later formed the matrix, was presented in the form of films and continuously brought together with the carbon fiber fleece. The polymer films were fed on two sides, although a one-sided feed is possible. After combining the polymer films and the carbon fiber nonwoven, the material was consolidated together by heated calenders or compacted or impregnated, the temperature here was 100 ° C above the glass transition temperature of the polymer used.

As a result, the polymer was introduced into the carbon fiber nonwoven and compacted to an organic sheet. The consolidated organo sheet was cooled down and wound up or sliced into sheets.

Variant 3 - Slurry impregnation by a) dipping, b) nozzle application, c) film transfer (including solvent)

In this variant, the matrix polymer was in the form of a suspension in a solvent. Water was used as the solvent, although an inorganic or organic solvent such as a ketone such as acetone or methyl ethyl ketone, an alcohol, an ether, an ester or the like, or a mixture of various solvents can be used as well. The solutions or suspensions optionally stabilizers, such as surfactants or water-soluble polymers, such as. As polyvinyl alcohol, but also other substances that cause stabilization of the suspension contain.

The coating system consisted of a respective unwinding unit for the carbon fiber fleece, a coating unit, a first calender, a furnace unit, a second calender, a cooling plate and a take-up unit.

The matrix was combined with the carbon fiber nonwoven in the following three different ways.

Subvariante 1 - Slurry - Diving:

In the Tauchimprägnierung with the suspension, the carbon fiber fleece was unwound, pulled for impregnation by a, the suspension-containing padding, squeezed off by metering rollers and fed into a dryer, in which the solvent was evaporated and the polymer was heated. The prepreg powder-coated by this impregnation was consolidated or compacted or impregnated through a heated consolidation section, namely in a calender, the temperature being 100 ° C. above the glass transition temperature of the polymer used.

As a result, the polymer was introduced into the carbon fiber fleece and compacted into a semifinished product, namely in a test series to form an organic sheet and in another test series into a prepreg. The consolidated semifinished product was finally cooled down and wound up or cut into slabs.

Subvariante 2 - Slurry nozzle order:

In the nozzle application of the suspension, the suspension was applied directly by means of a slot die on the carbon fiber fleece, passed through a calender for impregnation and then passed into a dryer in which the solvent was evaporated and the polymer was heated. The prepreg obtained by this impregnation was consolidated or impregnated by a heated consolidation line, namely a calender, the temperature being 100 ° C. above the glass transition temperature of the polymer used.

As a result, the polymer was introduced into the carbon fiber fleece and compacted into a semifinished product, namely in one test series to form an organic sheet and in another series of tests to form a prepreg. The consolidated semi-finished product was finally cooled down and wound up or sliced into sheets.

Subvariante 3 - Slurry - Film Transfer:

In this variant, the coating system consisted in each case of an unwinding unit for coating paper and the carbon fiber fleece, a coating unit, a first calender, a furnace unit, a second calender, a cooling plate and a take-up unit.

After applying the suspension to the coating paper with a very defined grammage of 115 g / m ² (+/- 3 g / m ² ), the carbon fiber nonwoven fabric was deposited in the resin film and consolidated in the first calender to a first impregnation. It was then passed to a dryer in which the solvent was evaporated and the polymer was heated. The prepreg obtained by this impregnation was consolidated or impregnated by a heated consolidation line, namely a calender, the temperature being 100 ° C. above the glass transition temperature of the polymer used.

As a result, the polymer was introduced into the carbon fiber fleece and compacted into a semifinished product, namely in one test series to form an organic sheet and in another series of tests to form a prepreg. The consolidated semi-finished product was finally cooled down and wound up or sliced into sheets.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• ASTM D5291-02 [0059]
• DIN EN 2557 [0062]
• DIN EN 2329 [0062]
• DIN EN 2559 [0062]
• ISO-14125 [0063]
• ISO-14125 [0063]
• ISO-14125 [0063]
• DIN / EN / ISO 1183-1 [0063]
• DIN / EN 2564 [0063]
• ASTM D5291-02 [0073]

Claims (17)

Process for producing a semifinished textile product, in particular a prepreg, from carbon fibers preimpregnated with a matrix material, which comprises the following steps: a) producing from at least 10% carbon fibers existing fleece and / or made of at least 10% carbon fibers felt, wherein at least a portion of the fibers used for the production of the fleece and / or felt are waste fibers and / or recycled fibers, and b) impregnating the web and / or felt with a matrix material selected from the group consisting of thermoplastics, thermosets, elastomers and any mixtures of two or more of the foregoing. A method according to claim 1, characterized in that the impregnation of the nonwoven and / or the felt with the matrix material in step b) is carried out by a process selected from the group consisting of prepreg process, wet pressing process, resin infusion process, film lamination process and vacuum supported (VARI) procedure. A method according to claim 2, characterized in that the impregnation of the web and / or the felt with the matrix material in step b) is carried out by a liquid prepreg process, by a powder prepreg process or by a wet pressing process. Method according to at least one of the preceding claims, characterized in that in step a) for the production of the fleece and / or the felt, a fiber mixture is used, which at least 20%, preferably at least 50%, particularly preferably at least 80%, more preferably at least 90%, most preferably at least 95% and most preferably entirely consists of waste fibers and / or recycled fibers. A method according to at least one of the preceding claims, characterized in that in step a) waste fibers and / or recycled fibers are used, of which at least 10%, preferably at least 30%, more preferably at least 60%, most preferably at least 80% and highest preferably 100% carbon fibers. Method according to at least one of the preceding claims, characterized in that in the step a) recycled fibers are used, which consist of waste in the form of fabric, scrim, knitted fabric, knitted fabric, pre-impregnated with a matrix material, fiber-containing composite material , in particular carbon fiber-containing composite material, or any mixture of two or more of the aforementioned materials. Method according to at least one of the preceding claims, characterized in that the fleece and / or the felt is used in combination with at least one other fibrous material, the other fibrous material being selected from the group consisting of woven fabrics, laid, unidirectional (UD-) Strands, tapes, nonwovens, felts and any mixtures of two or more of the aforementioned materials. A method according to claim 7, characterized in that the individual fiber materials are arranged in the form of a laminate, wherein the laminate consists for example of at least one nonwoven layer and at least one fabric layer or at least one nonwoven layer and at least one gel layer. A method according to claim 7 or 8, characterized in that as another fiber material at least partially composed of waste fibers and / or recycled fibers fiber material is used, which consists of carbon fibers, glass fibers, polymer fibers and mixtures of two or more of the aforementioned materials, wherein the polymer fibers are preferably Polyamide fibers, polyester fibers, polypropylene fibers, polyacrylonitrile fibers, oxidized polyacrylonitrile fibers, and fibers of copolymers of two or more of the foregoing materials and mixtures of two or more of the foregoing materials. Method according to at least one of the preceding claims, characterized in that in step b) a matrix material is used which is selected from the group consisting of epoxy resins, phenolic resins, vinyl ester resins, polyester resins, polyurethane resins, benzoxazine resins, novolaks, cyanate ester resins, bismaleimide resins, bisoxazolines , Polyolefins, such as polypropylene, engineering thermoplastics, such as polyamides, and any mixtures of two or more of the aforementioned materials. Method according to at least one of the preceding claims, characterized in that the fleece or the felt in step b) is impregnated with so much matrix material that the semi-finished product after step b) has a content of matrix material between 1 and 90 wt .-% , preferably between 30 and 70 wt .-% and particularly preferably between 40 and 65 wt .-%. Method according to at least one of the preceding claims, characterized in that the impregnation of the fleece and / or the felt with the matrix material in step b) is carried out by a powder prepreg process or by a liquid prepreg process, wherein the fleece or the felt before carrying out the process step b) on one or both sides with a carrier material, preferably with a carrier film or with a backing paper, is coated. Semifinished textile product, in particular prepreg, of carbon fibers preimpregnated with a matrix material obtainable by a process according to one of Claims 1 to 12. Carbon fiber reinforced composite material obtainable by curing or by thermal forming and optionally recompressing of a semi-finished textile product according to claim 13. Carbon fiber reinforced composite material according to claim 14, characterized in that it has a fiber content between 20 and 60%, preferably between 30 and 50%, more preferably between 35 and 45% and most preferably of 40%. Carbon fiber reinforced composite material according to claim 14 or 15, characterized in that it has a tensile strength of 100 to 2,000 N / mm ² and preferably from 200 to 800 N / mm ² and / or a modulus of elasticity of 5 to 180 GPa and preferably from 10 to 80 GPa having. Use of a semi-finished textile product according to claim 13 for the production of components, such as a structural component or an outer hull component of a motor vehicle, a rail vehicle or a transport vehicle.